With continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that is required to be dissipated immediately. Cooling fans are commonly used in combination with heat sinks for cooling the CPUs.
Referring to FIG. 12, a conventional cooling fan comprises a rotor 1 having a shaft 2 extending downwardly from a central portion of the rotor 1, a bearing 3 defining an inner hole for receiving the shaft 2 therein, and a frame 4. A central tube 5 is located at a middle portion of the frame 4. The bearing 3 impregnated with oil is secured in the central tube 5 to rotatably support the rotor 1. An oil retaining ring 6 is mounted around the shaft 2 and contacts a top end of the bearing 3 directly when the cooling fan is assembled.
During operation of the fan, the oil retaining ring 6 is rotated with the shaft 2. A friction is generated between the oil retaining ring 6 and the bearing 3, which results in a lot of heat being generated and temperature of the oil retaining ring 6 being raised. Due to the raise of temperature, the oil retaining ring 6 becomes easily aging and worn. When the oil retaining ring 6 is worn, it can no longer keep the oil from leaking out of the bearing 3, and the friction between the shaft 2 and the bearing 3 increases. Finally the useful life of the cooling fan is shortened.
What is needed, therefore, is a cooling fan having an improved oil sealing structure wherein during operating of the cooling fan, the oil retaining ring will not be subjected to friction with the bearing, and temperature of the oil retaining ring will not be raised.